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(-No Model.) 9 Sheets-Sheet 1. W. THOMSON. GALVANOMETER.

No. 416,654. Patented De0.'3, 1889.

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W. THOMSON. GALVANOMETER. i No. 416,654. Patented Dec. 3, 1889.

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GALVANOMETER.

No. 416,654. Patented Dec. 3, 1889.

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GALVANOMBTER. No. 416,664. Patented Dec. 3, 188.9.

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W. THOMSON.. GALVANOMETER N0. 416,654. P atented Dec. 3, 1889;

1 UNITED ST TES PATENT OFFIcE.

)VILLIAM THOMSON, OF GLASGOW, COUNTY OF LANARK, SCOTLAND.-

GALVANOM ETER.

SPECIFICATION forming part of Letters Patent No. 416,654, dated December3, 1889.

' Application filed December 8, 1887. Serial No. 257,320. (No model.)Patented in England y 10, 1886, No. 9,016 in France May23,1887,N0-183,730,andin Belgium May 25, 1887, No. 77,694.

To aZZ whom it may concern.-

Be it known that 1, Sir WILLIAM THOMSON,

knight, of Glasgow, in the county of Lanark, Scotland, have inventedcertain new and useful Improvements in Galvanometers, (for which LettersPatent have been granted to me in Great Britain, No. 9,016, dated July10, 1886; in France, No. 183,730, dated May 23, 1887, and in Belgium No.77,594, dated May 25, 1887,) of which the following is a specification.

My invention relates to apparatus for measuring the efficiency ofelectric currents; and it consists in certain features of novelty inapparatus designed for use in steady and undisturbed places.

The apparatus is an electro-dynamic balance consisting, essentially, ofa soft-iron core or movable coil made temporarily magnetic by thecurrent to be used by'means of a fixed coil or coils through which thecurrent temporarily passes. For a standard instrument not liable tochange with time I prefer a movable coil or coils mounted on agravity-balance and affected by corresponding fixed coil or coils andspecial arrangements for putting on or taking off weights.

My invention will be fully understood by reference to the accompanyingdrawings, in which Figure 1 is a front end elevation of the simi pleform of my invention as intended for land plan View of the simple form.

' the sliding weights.

use. Fig. 2 is a vertical longitudinal section on line 2 2, Fig. 7. Fig.3 is a vertical transverse section on line 3 3, Fig. 8. Fig. 4 is a Fig.5 isaside elevation of a modification in which the beam is mounted nearits center and has a coil at each end. Fig. 6 is aplan of the same. Fig.7 is a side elevation showing modifications in Fig. 8 is a plan view ofthe same. Fig. 9 is a further modification showing a balance suitablefor light work.

i represents the beam of the balance, which may be either supported onknife-edges or A suspended, in the'manner to be hereinafter described,near one end, and provided with a coilj at the other end, the weight ofthe coil and beam being counterpoised by a weight on the end of thelatter opposite to the coil. In this form I sometimes use a set ofweights space, as indicated in Fig. 7 and be supported by the stirrup p.This stirrup p is supported upon knife-edges q, as shown in Fig. 2.

' The suspended coil j is acted upon by one or more (preferably two)fixed coils w. (Sec Figs. 2 and 4.) These coils as may be either fiatand of approximately the same mean diameter as the suspended coil; andarranged as clearly shown in Figs. 5 and 6, or the coils may be ofcomparatively small depth in the direction of their diameters and ofsmaller cross-sections than the internal diameters of the suspendedcoils and fixed coaxially with them, so that their planes being paralleland nearly horizontal and at the proper distances apart give convenientelectro-dynamic stability. ferred when the instrument is intended to beused to measure powerful currents, and in such cases the coils are, fordirect-current measurements, made of copper ribbon of such The latterform of fixed coils is prebreadth and thickness as islconvenient forcarrying Without inconveniently heating the maximum current to bemeasured.

For alternating-current measurements both movable and fixed coils areconstructed of twisted copper rope made up of sufficiently thininsulated wire to prevent any disturbance which might result from theunequal distribution of the current over the cross-section of theconductor. The twist in the rope should be such that-there will be anintegral number of twists in the rope for each turn round the coil. Thesection of the rope is either round or flattened to a ribbon, as isfound most suitable in different cases. The coils are preferably woundon massive cop- 'per bobbins fixed in massive copper (or other plates,in consequence of their large surfaceand high thermal conductivityquality, facilitate the carrying away of the heat generated in the coilsby the passage of the" current, and hence prevent to a certain extenterror from this cause due to change of dimensions of the beam or upwardcurrents of air.

The preferred form for suspending the beam 1' is shown in Figs. 1 to 3.It consists of two flat ligaments .2, formed of a sui'ficient number ofvery fine wires laid side by side in the same plane. The two ends ofthis ligament are securely soldered to semi-cylindrical pieces a Z), theupper pair a of the pieces being fixed to the frame-work through thepillars c and cross-pieces d, and the lower pair 1) to the beam of thebalance. The beam is prevented from taking too much horizontal motion inthe direction of its length by means of forks e and steady-pins f,whereby the danger of bending the ligament z, and consequently changingthe zero-reading of the instrument, is avoided. The pins f are so placedas to be out of contact with the sides of forks c When the instrument isin use.

In Figs. 5 to 8 I have shown another form of my invention which I preferto use when the highest possible accuracy is desired. In this form thebeam of the balance is suspended from a point near the center of itslength. A coil j is attached to both ends of the beam, and each of thesecoils is acted upon by one or more fixed coils 0;, as will behereinafter described.

For the weights and lifters of the first form I substitute in this formeither scale-pans and weights or a slide g, fixed to the side of thebeam 2', along which weights h may be moved y sliders c", so as tobalance the electro-dynamic forces produced by the currents in thecoils. The sliders a" may be of the form shown in Figs. 5 and 6 or ofthe modified form shown in Figs. 7 and 8.

In the form shown iii Figs. 5 and 6 a rigid frame furnished with threefeet j slides along a horizontal platform fixed in front of theinstrument, said platform having formed along its length a V-shapedgroove, which forms a guide for two of the feetj. The slider 2" carrieson it a pivoted frame 75', held in an upright position by light springsZ. An upright piece m forming part of the frame passes through a recessin the weight, and when the weight is to be moved along the slide g theframe 70 is tilted over in the direction of mo tion and the whole framemoved until the weight is brought to the desired position, after whichthe frame lo is allowed to take an upright position and the bar massumes its position in the recess of the weight, as shown in Fig. 6,which leaves the weight clear and the balance free to move.

In the arrangement shown in Figs. 7 and 8 a pendant n is substituted forthe pivoted frame is, and the slider is moved from one side or the otherby threads 0', attached to the bottom of the pendant. When the weighthas been moved to the desired position, the thread is left slack, andthe pendant, by assuming a vertical position under the action ofgravity, falls to the center of the recess in the weight, which leavesthe beam free. The Weight on the right end of the "slide is intended tobe used as a counterpoi'se for the sliding weight when it is at its zeroposition, and also to give a convenient means for adjusting the beam ofthe balance to the zero position. For this purpose it is not necessarythat the frame which carries the pendant should be movable, as the rangeof movement of said pendant can be made sufficiently great to give therequired adj ustment.

On the slide 9 a scale of equal divisions is engraved and also a seriesof line notches corresponding in position to the lines of a second scale19, fixed to the frame-work of the instrument in a position above thebeam and at the back of the slide. These scales allow the position ofthe weights upon the slide to be read elf at any time. The numbers onthe fixed scale 19 are proportional to the square roots of the numberson the scale 9, and are such that when the weight is brought todifferent positions, so as to balance the electro-dynamie force due tothe different currents, equal differences of reading indicate equaldifferences of current. Side motion of the beam in this form of .theinstrument is prevented by the screws q. End mo tion is prevented bysimilar screws fixed to the frainework near the semi-cylindrical piecesI).

The form of instruments for measuring light currents (shown in Figs. 5.and G.) has lighter and longer suspension-ligaments at: tached to thebeam through a round central axis or trunnion, and is held from endmovement by passing this trunnion through a square hole in upright piece0", adjustably fixed to the base-plate of the instrument, or by twoscrews adjustably fixed on the two sides of the trunnion andguard-pieces fixed to the frame-work above the trunnion to prevent theligament from being so much slackened as to damage it. The arrangementwith graduated slide having self-relieving pendants to move the slidersis also applicable to ordinary weighing-balances.

IIO

When scale-pans are employed, I prefer, for convenience, to use twoscale-pans at each 7 end of the beam, one hung from'each of the fourprolongations or knife-edges at the ends of the transverse diameters ofthe coils.

hen no current is flowing through the coils, the whole or greater partof the weights should be placed on the scale-pan nearest the operatorand balance restored by weight placed in the most distant pan at theother end of the beam. The strength of current flowing at any timethrough thecoils is estimated by the amount of weight which has totransferred from one end of the beamto the other in order to restoreequilibrium.

Another modification of the balance which is suitable for a voltmeter isshown in Fig. 9. This form measures moderate changes of current by themovement of an index over a verbeam.

the electrical forces between the two coils as their distances apartvary. The necessary gravitational force against which the electrodynamicforce acts is obtained by adding the necessary weight to the movablecoil. It is preferable to place this weight as nearly as possible at'the transverse diameter of the coil; but in practice I have found itmore convenient to place the Weight (having the form of a round rod) ina V-shaped trough fixed to the outer end of the coil, with its length atright angles to the length of the balance- This form of balance isspecially suitable in conjunction with resistance-coils to indicate thechanges in potential which are being maintained on an electric circuit.

w in Fig. 15 represents a resistance-coil attached to the under side ofthe base-plate of the instrument.

Having thus described my invention,the following is what I claim as newand desire to secure by Letters Patent:

1. In an electro-dynamic balance, substantially as herein described, thecombination of beam 1', suitably suspended at one end, and coil at theother end, with stationary coil 00, surrounded by coil j, and suitableweights for attaching to said beam, whereby the dynamic force of thecurrents passed through said coils may be balanced and the difference intheir potentials measured, as set forth.

2. In an electro-dynarnic balance, substantially as herein described,the combination of the beam 2', the coil j, and ligamental suspensionforthe beam, whereby the current is led into and out of the circuit ofthe movable coil through said ligamental suspension,with stationary coilto and stirrup p for holding the weights, as set forth.

3. In an electro-dynamic balance, the combination of the beam 2' andcoils j and as with the graduated slide g, attached to the beam andadapted to support a sliding weight, whereby the electrical forces canbe balanced and their relative potentials measured, as hereinbeforedescribed.

at. In an electro-dynamic balance, the combination of the balance-beamand the movable and stationary coils with the massive copper or othermetallic base-plates and sup porting-bobbins, whereby the cooling of thecoils is effected, as hereinbefore described.

5. In an electro-dynamic balance, the combination of the coils and beamwith a scale of equal divisions and a square-root scale, whereby adirect reading of the strength of the current in circuit may be had, ashereinbefore described.

6. In an electro-dynamic balance, the combination of the coils, thebeam, and a scale with two slides carrying weights supported, on saidscale, one of which slides is adapted to adjust the zero of the balanceand the other to measure the current, as hereinbefore set forth.

7. In an electro-dynamic balance, the combination of the coils, thebeam, and scale on said beam with self -relieving pendants for movingthe weights along the slide, as hereinbefore described.

In testimony whereof I have signed my name to this specification in thepresence oftwo subscribing witnesses.

WILLIAM THOMSON. Witnesses: JOHN RENNIE, Private Secretary, 87 ParkRoad, Glasgow.

JAMES PoLLocH, Butler to Sir Wm. Thomson, University Gardens, HiZZhead.i

